Project Summary: Bacterial microcompartments are large subcellular structures composed of metabolic enzymes encapsulated within a protein shell built from multiple subunits. They are widespread among bacteria, functionally diverse, linked to pathogenesis, have a number of important potential biomedical applications, and appear to incorporate unique mechanistic and structural principles. Their function is to sequester and regulate the production of toxic or volatile intermediates found in certain metabolic pathways. However, little is known about how this is occurs at the mechanistic level. The long-term goal of the proposed research is to elucidate the molecular principles and to build up a 3-dimensional structure of the microcompartments involved in 1,2-propanediol degradation by Salmonella. The Salmonella system is unmatched with regard to the knowledge and tools available for mechanistic studies of microcompartments. The proposed studies combine genetic, biophysical, and structural methods to elucidate the cellular function of the Salmonella Pdu microcompartment at a mechanistic level. Three specific aims are proposed: 1. Determine the role of terminal helixes and other mechanisms for targeting proteins to the lumen of the Pdu microcompartment; 2. Determine the role of pores and cofactor recycling in supplying the lumen enzymes of the Pdu microcompartment with required substrates and cofactors; and 3. Elucidate the higher order structure and assembly of the Pdu microcompartment. Structures will be investigated and analyzed by x-ray crystallography, biophysical, and computational methods. Protein-protein binding studies will include his-tag pulldowns, biophysical methods, and crystallography. Functional and mechanistic insights will be derived from structure-guided mutagenesis in conjunction with genetic and biochemical studies. Completion of the proposed investigations will elucidate the mechanistic and structural principles of the Salmonella pdu microcompartment. This will provide general insights into bacterial microcompartments. Since bacterial microcompartments play critical metabolic roles in many microbes, including several human pathogens, the proposed studies may ultimately lead to new opportunities for interfering with pathogenic processes.